Sealed and thermally insulated vessels for storing liquefied natural gas that are built into a load-bearing structure, such as the double hull of a ship used to transport liquefied natural gas are known in the prior art. Such vessels usually have a multi-layer structure having, successively arranged through the thickness of the vessel from the outside towards the inside of the vessel, a secondary thermal insulation barrier attached to the load-bearing structure, a secondary sealing membrane bearing against the secondary thermal insulation barrier, a primary thermal insulation barrier bearing against the secondary sealing membrane and a primary sealing membrane designed to be in contact with the liquefied natural gas contained in the vessel.
Document FR 2996520 describes a secondary sealing membrane formed by a plurality of metal sheets having corrugations projecting towards the outside of the vessel, thereby enabling the secondary sealing membrane to be deformed by the thermal and mechanical stresses generated by the fluid stored in the vessel. The secondary thermal insulation barrier is made up of a plurality of insulation panels juxtaposed against the load-bearing structure. The insulation panels of the secondary thermal insulation barrier are separated by interstices into which the corrugations of the metal sheets of the secondary sealing membrane are inserted. Furthermore, the metal sheets of the secondary sealing membrane are welded to metal plates attached to the inner face of insulation units of the secondary thermal insulation barrier such as to anchor the secondary sealing membrane to the secondary thermal insulation barrier.
When cooling the vessel, i.e. when the vessel is filled with liquefied natural gas, the insulation panels of the secondary thermal insulation barrier tend to retract and, consequently, to move apart from one another. The insulation panels may also move apart from one another as a result of deformation of the double hull of the ship. The separation of the insulation panels of the secondary thermal insulation barrier generates significant stresses on the secondary sealing membrane. Furthermore, such separation stresses the secondary sealing membrane all the more since the latter is sandwiched between the insulation panels of the secondary thermal insulation barrier and the insulation panels of the primary thermal insulation barrier, said separation of the insulation panels causing the secondary sealing membrane to rub against the insulation panels of the primary and secondary thermal insulation barriers.
Document WO2013004943 provides a secondary sealing membrane made up of a plurality of corrugated metal sheets having corrugations projecting towards the outside of the vessel, which is attached to couplings directly connected to the load-bearing structure. Thus, since such a secondary sealing membrane is not attached directly to the insulation panels of the secondary thermal insulation barrier, same is not mechanically affected by the insulation panels moving apart from one another. However, such a design is also unsatisfactory. Indeed, such an attachment of the secondary sealing membrane to couplings only provides sporadic links to the secondary sealing membrane, and as a result same is not stressed uniformly. Furthermore, since the secondary sealing membrane is sandwiched between the insulation panels of the secondary thermal insulation barrier and the insulation panels of the primary thermal insulation barrier, the reciprocal separation of the insulation panels of the secondary thermal insulation barrier nonetheless generates a mechanical stressing of the secondary sealing membrane as a result of the friction caused between same and the insulation panels of the secondary thermal insulation barrier.
Abstract
One idea at the heart of the invention is to propose a sealed and thermally insulated vessel fitted with a secondary sealing membrane comprising a plurality of metal sheets having corrugations, in which said secondary sealing membrane is subjected to low-intensity, uniform stresses, in particular when cooling the vessel.
According to one embodiment, the invention provides a sealed and thermally insulated vessel for storing a fluid, comprising a secondary thermal insulation barrier comprising insulation panels held against a load-bearing structure and anchored to same by secondary retaining members, a secondary sealing membrane carried by the insulation panels of the secondary thermal insulation barrier, a primary thermal insulation barrier anchored against the secondary sealing membrane by primary retaining members and a primary sealing membrane carried by the primary thermal insulation barrier and designed to be in contact with the cryogenic fluid contained in the vessel;
the secondary sealing membrane comprising a plurality of corrugated metal sheets sealingly welded to one another, each having at least two perpendicular corrugations;
the insulation panels of the secondary thermal insulation barrier being juxtaposed, each insulation panel having an inner face opposite the load-bearing wall, said inner face being fitted with metal plates onto which the corrugated metal sheets are welded;
each insulation panel being associated with adjacent insulating panels by means of a plurality of bridging elements, each bridging element being arranged to straddle at least two adjacent insulating panels and being attached firstly to one edge of the inner face of one of the two insulation panels and secondly to a facing edge of the inner face of the other insulation panel such as to prevent the adjacent insulation panels from moving apart from one another.
Thus, the bridging elements provide a mechanical link between the insulation panels of the secondary thermal insulation barrier that prevents the insulation panels from moving apart from one another such that the secondary sealing membrane is less stress than the secondary sealing membranes in vessels in the prior art, in particular when cooling the vessel.
According to the embodiments, such a vessel may have one or more of the following features:                the edges of the inner faces of each of the adjacent insulating panels that are straddled by a plurality of bridging elements face one another. In other words, said edges of each of the insulation panels are adjacent.        the corrugations of the corrugated metal sheets of the secondary sealing membrane project towards the outside of the vessel and towards the load-bearing structure, the inner face of the insulation panels of the secondary thermal insulation barrier having perpendicular slots designed to receive the corrugations of the corrugated metal sheets.        the corrugations of the corrugated metal sheets of the secondary sealing membrane project towards the inside of the vessel, the primary thermal insulation barrier having insulation panels, each of which has an outer face with perpendicular slots designed to receive the corrugations of the corrugated metal sheets of the secondary sealing membrane.        the bridging elements are bridging plates that each have an outer face bearing against the inner face of each of the adjacent insulation panels and an inner face carrying the secondary sealing membrane.        the inner face of the insulation panels has recesses formed along the edges of said inner face, and the bridging plates are attached to the inside of said recesses.        the bridging plates are as thick as the recesses are deep.        the bridging plates are attached by bonding, screwing and/or stapling against the inner face of each of the two adjacent insulation panels.        the bridging plates are made of plywood.        each insulation panel has a rectangular parallelepiped shape and has an inner face including two series of slots designed to receive the corrugations of the corrugated metal sheets, each of the two series of slots being perpendicular to the other series and to two opposite sides of the insulation panel, the plurality of bridging elements including, along each edge of the inner surface of each insulation panel, a bridging element arranged in each gap between two consecutive slots in the series of slots perpendicular to said edge.        each insulation panel has a rectangular parallelepiped shape and has an inner face including two series of slots designed to receive the corrugations of the corrugated metal sheets, each of the two series of slots being perpendicular to the other series and to two opposite sides of the insulation panel, the plurality of bridging elements including, along each edge of the inner surface of each insulation panel, a bridging element having a series of slots extending the series of slots perpendicular to said edge.        the bridging element comprising a series of slots extending the series of slots perpendicular to said edge also includes a slot perpendicular to said series of slots.        the secondary thermal insulation barrier has a bridging element at each corner of the inner face of each insulation panel straddling said corner of said insulation panel and the neighboring corner of the inner face of each of the two or three adjacent insulation panels.        a bridging element includes an elongate element, such as a wire or a flexible blade element, that is rigidly attached to two attachment members attached respectively to each of the two adjacent insulation panels.        a bridging element is formed by two metal plates each having a folded edge forming a flange, the flanges being respectively held inside a slot formed in the inner face of each of the two adjacent panels, the two metal plates being attached together by attachment members.        each insulation panel has a layer of insulating polymer foam and a rigid inner plate forming the inner face of said insulation panel.        the insulating panels are separated from one another by interstices, the secondary thermal insulation barrier having an insulating blanket arranged in the interstices.        the insulating blanket arranged in the interstices between the insulation panels is a porous blanket designed to allow gas to flow through the interstices.        the primary sealing membrane has a plurality of corrugated metal sheets welded to one another and each having at least two perpendicular corrugations projecting towards the inside of the vessel and the primary thermal insulation barrier has a plurality of juxtaposed insulation panels, each insulation panel having an inner face fitted with metal plates onto which the corrugated metal sheets of the primary sealing membrane are welded.        
Such a vessel may be part of an onshore storage facility, for example for storing LNG, or be installed on a coastal or deep-water floating structure, notably a liquefied natural gas carrier, an ethane carrier, a floating storage and regasification unit (FSRU), a floating production, storage and offloading (FPSO) unit, inter alia.
According to one embodiment, a ship used to transport a cold liquid product has a double hull and the aforementioned vessel arranged in the double hull.
According to one embodiment, the invention also provides a method for loading onto or offloading from such a ship, in which a fluid is channeled through insulated pipes to or from an onshore or floating storage facility to or from the vessel on the ship.
According to one embodiment, the invention also provides a transfer system for a fluid, the system including the aforementioned ship, insulated pipes arranged to connect the vessel installed in the hull of the ship to an onshore or floating storage facility and a pump for driving a fluid through the insulated pipes to or from the onshore or floating storage facility to or from the vessel on the ship.